The systemic hemodynamic state of a mammal is defined by the relationship between blood pressure and global blood flow at the output node of the left heart. The normal hemodynamic state can be altered as a result of conditions such as congestive heart failure and essential hypertension, and secondary to trauma and surgery.
Blood pressure and global blood flow are determined in turn by several interrelated systemic hemodynamic modulators. These modulators include intravascular volume (volemia), inotropy, vasoactivity and chronotropy.
In general, blood pressure is used as the major indicator of systemic hemodynamic state because blood pressure has been measured easily and non-invasively for many decades using sphygmomanometry and because physicians have been trained to rely on it. However, using blood pressure as the major indicator of systemic hemodynamic state can lead to incomplete and inaccurate diagnoses and to inappropriate therapeutic measures.
The primary function of the cardiovascular system in mammals is the transport of oxygen. Oxygen transport is related to global blood flow (stroke index and cardiac index), like the systemic hemodynamic state but, unlike the systemic hemodynamic state, is not related to blood pressure.
Measurement of global blood flow to determine a patient's oxygen transport or hemodynamic state can be made either invasively by the thermodilution method or noninvasively using Thoracic Electrical Bioimpedance. Unfortunately, the availability of methods of monitoring global blood flow has not changed the hemodynamic and oxygen transport management of patients. There are several reasons for this failure. First, physicians still tend to rely solely on blood pressure measurements to make diagnoses and to make therapeutic decisions concerning a patient's hemodynamic state and oxygen transport. Second, medical education has not absorbed recent advances in the noninvasive measurement of global blood flow. Therefore, physicians graduate without a clear understanding of the role that global blood flow measurements can have in diagnosis and treatment of defects in oxygen transport. Lacking this understanding, physicians incorrectly target symptoms such as hypertension or a low flow state for therapeutic intervention rather than identifying and therapeutically correcting abnormal levels in the systemic hemodynamic modulators which are the underlying causes.
Further, current cardiovascular care is primarily reactive to catastrophic events rather than preventive. This approach has led to substantial failures in diagnosis and treatment. For example, it is estimated that death is the first indication of a cardiovascular disorder in 40% of persons.
Therefore, it would be advantageous to have a method of diagnosing and treating cardiovascular disorders based on an understanding of the relationship between the systemic hemodynamic state and systemic hemodynamic modulators. Further, it would be advantageous to have a method utilizing information on global blood flow to determine and treat specific causes of cardiovascular disorders. Also, it would be useful to have an automated system utilizing these methods.